What is the ruling on girls showing a small part of the front of their hair while adhering to loose Islamic dress and hijab, and covering their faces when they feel that they have become attractive to young men, and is it permissible to accuse them of bad character?

A Muslim woman must wear a full, concealing hijab (definition) covering her entire body when going out or in the presence of a non-mahram (definition) man. This includes covering all the hair on her head, as it is 'awrah (private parts that must be covered) that must be concealed from non-mahram men, by the consensus of scholars. An exception to this is when they are alone in their homes or in the presence of mahrams (unmarriageable kin). Girls who do not adhere to this must be advised while their shortcomings are concealed.